Containers of a polyester as represented by polyethylene terephthalate (PET) feature excellent properties such as transparency, heat resistance, gas-barrier property and the like, and have been extensively used for a variety of kinds of applications.
In recent years, on the other hand, it is a mounting demand to reutilize resources, and attempts have been made to recover the used containers inclusive of the above polyester containers and to reuse them as the recycled resin for various applications. Here, many of the contents contained in the packing containers are subject to be degraded with light, as represented by some kinds of beverages, medicines, cosmetics and the like. Therefore, these kinds of contents are provided being contained in opaque containers that are formed by using a resin composition of a resin blended with a coloring agent such as pigment. From the standpoint of reutilizing the resources, however, adding the coloring agent is not desired (since it makes it difficult to maintain transparency in the recycled resins). Therefore, it has now been demanded to use transparent containers. Accordingly, even those opaque containers suited for containing photo-degradable contents must be improved for their properties so as to be used again.
In order to impart light-shielding property (opaqueness) without using coloring agent, it can be contrived to realize a foamed container by making bubbles present in the container wall. A variety of proposals have been made concerning such foamed plastic containers. For instance, a patent document 1 discloses a foamed plastic container proposed by the present inventors and having a container wall in which foamed cells are distributed being flattened by the stretching, the flat foamed cells having lengths in the axial direction of the container (in the direction of a maximum stretch) that are decreasing from the outer surface of the container toward the inner surface thereof.